1) Field of the Invention
The present invention relates to a forming part of paper making machine, including a twin-wire former, an on-top former and a multilayer former, which is designed to let a stock (material liquid of paper) run through a paper production gap defined between two wires while drying it.
2) Description of the Related Art
A twin-wire former has been known as one of sheet forming apparatus for use in paper machines. This twin-wire former is equipped with two mesh-like wires each shaped into a loop configuration. While a stock travels between these two wires in a state put there between, various types of drainage equipments (extractors) remove the moisture from the stock, thereby gradually forming a fibrous mat, which grows into a web.
For example, FIG. 6 illustratively shows a construction of one example of a twin-wire former. With reference to this illustration, a description will be given here in below of a twin-wire former.
As FIG. 6 shows, a stock 2 from the lip of a head box 1 is jetted toward a gap (paper production gap) 15 (see FIG. 7) defined between two mesh-like wires of a first wire (#1 wire) 3 and a second wire (#2 wire) 4.
The first wire 3 is guided by a forming roll 16, a guide roll 18 and others while the second wire 4 is guided by a breast roll 17, guide rolls 19A to 19C and others, with these wires 3 and 4 being situated to define the gap 15 there between. The stock 2 grows into a fibrous mat while traveling in this gap 15.
That is, the upper and lower wires 3 and 4 are rotationally driven to convey the stock 2 in the gap 15 in a predetermined direction (upwardly in FIG. 6), and the stock 2 travels in the gap 15 at a speed approximately equal to those of the wires 3 and 4. The gap 15 is gradually made narrower toward the downstream side in the traveling direction, and the loop of each of the wires 3 and 4 at the upstream section of the gap 15 is placed on a curved surface with a radius of curvature R. Moreover, a first drainage equipment 5, a second drainage equipment 6 and a third drainage equipment 7 are provided in the order at the upstream section of the gap 15, while a suction couch roll 8 and others are located on the downstream side of these drainage equipments.
The first drainage equipment 5 is put in the loop of the second wire 4 which has a radius of curvature R. As FIG. 7 shows, in this first drainage equipment 5, a plurality of dewatering blades 20a to 20e (which will be designated at numeral 20 if they are not required to be distinguished from each other) are spaced from each other, and the bottom wire 4 is brought into sliding contact with the top surface (front surface) of each of the dewatering blades 20 to travel to draw a loop with a radius of curvature of R, while the top wire 3 also travels along a loop having a radius of curvature of approximately R in a state in which the stock 2 is put therebetween.
While the stock 2 travels along the curved gap approximate to the radius of curvature R, it grows gradually into a fibrous mat in the gap 15 due to the drainage (see arrows headed “white water” in FIG. 8) to both sides (upper and lower wires 3, 4 sides) by the dewatering pressures stemming from the bending along the radii of curvature of the top wire 3 and the bottom wire 4 on the dewatering blades 20. Incidentally, although being fixedly secured through key slots, made in their rear surfaces, to a proximal portion of the first drainage equipment 5, each of the dewatering blades 20a to 20e is made to be attachable/detachable thereto/therefrom in the wire width (cross) directions to be individually replaceable according to paper production conditions or the like.
The second drainage equipment 6 is placed within the loop of the first wire 3 which has a radius of curvature of R, and although not shown in detail, it is equipped with a plurality of inhibited dewatering blades which control the drainage toward the first wire 3 side but allows the drainage toward only the second wire 4 side, thus forming a web gradually.
The third drainage equipment 7 is equally called “suction box”, and is located within the loop of the second wire 3. Through the use of the third drainage equipment 7 and the suction couch roll 8, the drainage is made by means of vacuum, and a web formed through a transfer box (not shown) is transferred onto the second wire 4 and conveyed through a suction pickup roll (not shown) to the next press part.
In addition, a paper layer forming apparatus for a paper machine further includes, for example, an on-top former and a multilayer former. The on-top former or the multilayer former is equipped with a bottom wire extending throughout the upstream and downstream of the former and partially equipped with a top wire located at an intermediate section of the former. In this section, as well as a twin-wire former, the bottom wire and the top wire converge (are brought closer to each other) to define a paper production gap.
For example, FIG. 9 is a side elevational view illustratively showing an intermediate section of a multilayer former. As FIG. 9 shows, a stock is injected from a head box (for example, a first head box; not shown) located on the upstream side of the to form a layer (for example, a first layer) 2A and a stock is injected from a head box (for example, a second head box) 1B to form a layer (for example, a second layer) 2B in piles on the layer 2A, and after running through a paper production gap defined between a bottom wire 3 and a top wire 4, these layers 2A and 2B are formed into a multilayered web. In this illustration, only two layers are shown, but sometimes further layers are formed thereon by further injection of stocks.
In this connection, drainage equipments 5′, 6′ and 7′ are placed at a landing position of the stock, the top wire 4 position and a downstream side position thereof, respectively. Moreover, the top wire 4 are guided by guide rolls 8′ and 9′.
Also in the case of an on-top former, as well as the multilayer former shown in FIG. 9, a top wire 4 is placed at an intermediate section, but the second head box 1B is not put to use in this case, so the stock grows into a single layer.
Meanwhile, in the case of a twin-wire former, a jetted stock (which will hereinafter be referred to equally as a “material jet”) 2 injected from a head box 1 is directed at a gap 15 between both wires 3 and 4, and in detail, as FIG. 8 shows, it lands in the vicinity of an upstream end of a first drainage equipment 5 and in the vicinity of a portion at which both the wires 3 and 4 converge.
That is, both the wires 3 and 4 are made to approach each other at an upstream end of a dewatering blade (which is called a “lead-in blade”) 20a lying on the most upstream portion of the first drainage equipment 5 so that the gap 15 therebetween reaches a predetermined distance. The material jet 2 is injected to be directed at the place where both the wires 3 and 4 are brought closer to each other; in consequence, for example, the material jet 2 arrives at a landing point 10 on the first wire 3 while arriving at a landing point 11 on the second wire 4.
As FIG. 8 shows, the landing point 11 on the second wire 4 is positioned on the upstream side of the lead-in blade 20a. This is because, since the lead-in blade 20a has a solid construction (having no opening), the arrival of the material jet 2 on a surface of the lead-in blade 20a makes it difficult to remove an air layer incident to a plane of the material jet 2 and this air layer disturbs the material jet 2 to hinder the formation of a paper layer so that the paper production becomes unfeasible.
For this reason, the landing point 11 on the second wire 4 is set on the upstream side of the lead-in blade 20a, and in a case in which the material jet 2 lands on the wire at a portion of the traveling wire, particularly, where a guide, such as a blade, does not exist on the rear surface side thereof, if an angle β0 made between the material jet 2 and the wire (in this case, the second wire 4) is made large, the reactive force against the landing of the material jet 2 increases to cause the deflection of the wire; as a result, for example, the disturbance occurs in the flow of the opposite plane of the material jet 2, that is, the wire 3 side material jet plane, to obstruct the formation of the paper layer. Accordingly, it is impossible to set the angle β0 between the material jet 2 and the wire to a large value.
In consequence, the convergent angle between both the wires 3 and 4 is required to be made smaller to decrease the angle β0 made between the material jet 2 and the wire, whereas the decrease in the angle β0 made between the material jet 2 and the wire causes the position of the landing point 11 on the second wire 4 to largely vary simply by changing the direction of the material jet 2 slightly, and the positional adjustment (that is, the landing adjustment) of the landing point (in particular, the landing point 11 on the second wire 4) becomes more difficult as the operating speed of the paper machine becomes higher.
If the landing point 11 of the material jet 2 comes to a surface of the lead-in blade 20a, since the air layer incident to the plane of the material jet 2 disturbs the material jet 2 as mentioned above to hinder the formation of a paper layer, for example, defects on paper, including spotting (a phenomenon that a portion with no fibers appears on a surface of paper due to the entrainment of air) tends to occur more frequently as the operating speed of the paper machine increases. For this reason, there is a need to achieve the landing adjustment with high accuracy.
In addition, the decrease in the angle β0 made between the material jet 2 and the second wire 4 causes the greater fluid wedge effect to take place between the material jet 2 and the second wire 4 as the operating speed of the paper machine becomes higher, and this fluid wedge effect produces a static pressure in a space between the material jet 2 and the second wire 4 to induce the disturbance of the plane of the material jet 2 (the interface between the material jet 2 and the air), which leads to easier occurrence of the paper defects including the aforesaid spotting.
Still additionally, also in a case in which the landing point 11 on the second wire 4 is positioned on the upstream side of the lead-in blade 20a, the landing point 10 on the first wire 3 is positioned in the vicinity of the upper end portion of the lead-in blade 20a at which both the wires converge, and the landing point 10 on the first wire 3 and the landing point 11 on the second wire 4 are shifted by a difference α0 from each other in the direction of the flow of the material jet 2 so that difficulty is experienced in conducting the simultaneous drainage in a section (the difference α0 section) from the landing point 11 on the second wire 4 to the landing point 10 on the first wire 3. The difficulty of the simultaneous drainage makes it difficult to secure the homogeneity of the surfaces of the paper layer on both sides of paper, and in particular, as the operating speed becomes higher, the degree of difficulty in securing the paper quality increases accordingly.
Meanwhile, in the case of a twin-wire former, with an increase in paper production speed, combined with the above-mentioned problems resulting from the material jet landing point, there exist requirements for the improvement of the dewatering performance including the enhancement of the dewatering ability of each drainage equipment (that is, increase in drainage quantity) and the improvement of the drainage balance between both the surfaces of paper.
Such enhancement of drainage performance effectively eliminates the troubles stemming from the aforesaid landing of the material jet 2, such as securing the aforesaid homogeneity of the paper layer surfaces or suppressing the occurrence of paper defects including the aforesaid spotting. That is, it is a significant object to improve the paper quality under the condition of high-speed operation.
Moreover, this requirement for the enhancement of the drainage performance exists with respect to not only the drainage equipment existing at the upstream end of the twin-wire former and in the vicinity of the material jet landing point but also each of the drainage equipments on the downstream side thereof.
Still moreover, not only to the twin-wire former, for example, but also to the on-top former or the multilayer former (see FIG. 9) in which the paper production gap defined in a manner that two wires converge is made in an intermediate section of the paper former, it is a significant object to enhance the drainage performance of each of the drainage equipments for improving the paper quality.